Although bone marrow transplantation (BMT) would offer a cure to many patients with hemoglobinopathies, current preparative regimens for BMT are so toxic that few patients are offered this option until they have developed severe, and often irreversible complications of their disease. In addition, many patients do not have a suitable HLA-matched donor, and therefore do not have this therapeutic option. In this laboratory, we have previously demonstrated in mice that the induction of mixed chimerism provides a mode of hematopoietic reconstitution which involves much less toxic preparative regimens and may be applicable across MHC barriers. The overall objective of this research proposal is to extend our studies of mixed lymphohematopoietic chimerism to miniature swine in order to provide a large animal preclinical model to study the application of this modality to the cure of hemoglobinopathies. Specifically, we intend to: 1) Extend our non-myeloablative regimen for the induction of mixed chimerism, utilizing sublethal whole body irradiation, to miniature swine; 2) Determine the potential of very high doses ("megadoses") of PBSC to achieve mixed chimerism and tolerance without irradiation; 3) Study parameters involved in determining the relative reconstitution of lymphoid, myeloid and erythroid precursors following the induction of mixed chimerism; and 4) Determine the mechanism(s) of mutual tolerance induction in host and donor T cell populations following the induction of mixed chimerism. Our preliminary data indicate feasibility of all of these aims, and suggest that the miniature swine model may permit us to design a clinically applicable protocol for the use of mixed chimerism in the treatment of hemoglobinopathies.